Geology, geochemistry, mineralogy and genesis of the Spetsugli high-germanium coal deposit in the Pavlovsk coalfield, Russian Far East

The geology, mineralogy, and geochemistry of the Spetsugli high-germanium coal deposit in the Pavlovsk coalfield were studied. The deposit is characterized by the complex polyelemental composition of the ores and can be evaluated as a complex rare metal-coal deposit. The metal-bearing coals of the deposit are characterized by abnormally high, tens or even hundreds of times greater than the mean contents for brown coals of the world, for Ge, Sb, Hg, W, Li, Be, Cs, and As. Somewhat less anomalous are the levels of accumulation of U, Mo, Y, Rb, medium and heavy lanthanides, Zn, and Ga. Detailed mineralogical and geochemical characteristics of the germanium mineralization and associated anomalous concentrations of W, Sb, Hg, As Li, Be, Cs, U, Mo, Y, Rb, and HREE are described in the paper. The variations in concentrations were studied in vertical profiles and laterally. Complex mineralogical-geochemical and geological-structural analysis of the composition and structural features of the Spetsugli Ge-coal deposit allow us to revise the accepted hydrothermal model of the Ge mineralization formation in coals and substantiate the previously proposed hypergenic model for deposits of this type. The new data are in good agreement with the hydrogenic hypergenic model of the formation of complex Ge coal deposits where the source of metals is the basement rocks or the coal-bearing depression margins. The formation of the Ge and associated mineralization in the Spetsugli deposit was controlled by the weathering crust formation on hydrothermally altered rare metal granites of the Voznesenk Complex, broken through by the Late Permian dikes. The isotopic ages of the granites (448.2 Ma) and dikes (263.6 Ma) were determined and also the rhyolitic tuffs (25.1 Ma) which overlie the Eocene-Oligocene coal-bearing sediments in the basin. The isotopic age of the granites (448.2 Ma), dikes (263.6 Ma), and rhyolite tuffs overlapping the carbonaceous deposits (25.1 Ma) was determined. The rare metal mineralization is related to the basement protrusion in the centre of the deposit, forming a concentric-zone halo of Ge and associated elements around it. The basement protrusion granites were hydrothermally altered to form quartz-albite-microcline metasomatites and greisen containing the W-Mo and Hg-Sb-As mineralization. The metasomatically altered granites and dikes were transformed into a kaolin weathering crust as a result of late hypergenic alterations, with destruction of primary endogenous mineralization and removal of major elements to the surrounding paleopeatlands. Both types of endogenous mineralization in granites and dikes have anomalous accumulation of W, Mo, Sb, Hg, As, Li, Rb, Cs, Be, U, Y, lanthanides, Zn and Ga in the germanium-bearing coals during the Eocene-Oligocene time.

Automated summary

The geological, mineralogical, and geochemical characteristics of the Spetsugli high-germanium coal deposit were studied, revealing a complex polyelemental composition with metal-bearing coals containing abnormally high levels of various elements. The formation of germanium mineralization and associated anomalous concentrations of elements in the deposit was controlled by weathering crust formation on hydrothermally altered rare metal granites, supporting a hypergenic model for deposits of this type.